Flat-panel displays are widely used in conjunction with computing devices, in portable devices, and for entertainment devices such as televisions. Such displays typically employ a plurality of pixels distributed over a display substrate to display images, graphics, or text. In a color display, each pixel includes light emitters that emit light of different colors, such as red, green, and blue. For example, liquid crystal displays (LCDs) employ liquid crystals to block or transmit light from a backlight behind the liquid crystals and organic light-emitting diode (OLED) displays rely on passing current through a layer of organic material that glows in response to the current. Displays using inorganic light emitting diodes (LEDs) are also in widespread use for outdoor signage and have been demonstrated in a 55-inch television.
The various light-emitting technologies have different characteristics, advantages, and disadvantages. For example, liquid crystals are simple to control and have a highly developed and sophisticated technological infrastructure. Organic LEDs are area emitters, can be more efficient and flexible, and are demonstrated in a very thin form factor. Inorganic light-emitting diodes are very efficient and provide relatively saturated light in an environmentally robust structure. Lasers are also efficient, provide a virtually monochromatic light, but have a limited viewing angle. None of these technologies, however, meet all of a display viewer's needs under all circumstances.
In any application requiring many elements, it is important that each element is reliable to ensure good manufacturing yields and performance. Active-matrix control circuits, as well as the controlled element (e.g., a light emitter) are subject to failure. Because no manufacturing process is perfect, any large system can have defective elements. To ensure that large multi-element systems are reliably manufactured and operated, some systems employ identical, redundant elements. For example, displays are sometimes designed with redundant light emitters. U.S. Pat. No. 5,621,555 describes an LCD with redundant pixel electrodes and thin-film transistors to reduce defects. In another approach described in U.S. Pat. No. 6,577,367, an extra row or column of pixels is provided to replace any defective row or column.
An alternative approach to improving display yields uses additional, redundant light-emitting elements, for example two light emitters for every desired light emitter in the display. U.S. Pat. No. 8,766,970 discloses a pixel circuit with two sub-pixels and circuitry to determine whether a sub-pixel is to be enabled, for example if another sub-pixel is faulty. Similarly, U.S. Pat. No. 7,012,382 teaches an LED-based light system that includes a primary light source and at least one redundant light source. The primary light source is activated by itself and the performance of the light source is measured to determine whether or not to drive the redundant light source. The redundant light source is activated when the performance measurements indicate that a performance characteristic is not being met by the primary light source alone. The first light system can be activated in combination with the redundant light source once the decision is made to activate the redundant light source. U.S. Pat. No. 8,791,474 discloses redundant pairs of micro LED devices driven by a common transistor. WO 2014149864 describes separately controlled LED devices. However, such redundant systems, although they can improve yields, do not meet a wider variety of needs in a display.
There is a need, therefore, for a display system that can meet a wider variety of needs in a greater variety of viewing circumstances.